Turbine engines are used as the primary power source for various kinds of aircrafts. The engines may also serve as auxiliary power sources that drive air compressors, hydraulic pumps, and industrial gas turbine (IGT) power generation. Further, the power from turbine engines may be used for stationary power supplies such as backup electrical generators for hospitals and the like.
Most turbine engines generally follow the same basic power generation procedure. Compressed air is mixed with fuel and burned, and the expanding hot combustion gases are directed against stationary turbine vanes in the engine. The vanes turn the high velocity gas flow partially sideways to impinge on the turbine blades mounted on a rotatable turbine disk. The force of the impinging gas causes the turbine disk to spin at high speed. Jet propulsion engines use the power created by the rotating turbine disk to draw more air into the engine and the high velocity combustion gas is passed out of the gas turbine aft end to create forward thrust. Other engines use this power to turn one or more propellers, electrical generators, or other devices.
Because fuel efficiency increases as engine operating temperatures increase, turbine engine blades and vanes are typically fabricated from high-temperature materials such as nickel-based and cobalt-based superalloys. However, although nickel-based superalloys have good high temperature properties and many other advantages, they are susceptible to corrosion, oxidation, thermal fatigue and erosion damage in the high temperature environment during turbine engine operation. In such cases, the turbine nozzle guide vanes may need to be repaired, such as, by a brazing process.
Brazing processes typically employ a braze alloy mixture that includes a high-melt alloy and a low-melt alloy. The high-melt alloy usually is substantially similar to or better than the component alloy being repaired. The low-melt alloy typically comprises a braze alloy powder that has a lower melting temperature than the high-melt alloy and a relatively small amount of gamma prime and solid solution strengthening alloying elements, which contribute to elevated-temperature properties in brazing repaired components. When the braze alloy mixture is applied to a repair area on the turbine component and subjected to heat in a vacuum furnace, the mixture melts and heals cracks or buildup materials on the repair area. However, it has been found that because currently known braze alloys contain a relatively small amount of gamma prime and solid solution strengthening elements, the metallurgical integrity and performance of the repaired components may be inferior to the metallurgical integrity of the base materials under circumstances in which the repaired components are subjected to the elevated temperatures and high-stress loads during engine operation.
Hence, there is a need for improved materials for repairing turbine engine components such as the turbine nozzles and vanes. There is a particular need for repair materials that will improve a turbine component's durability, and for efficient and cost effective methods of repairing the components using such materials.